Beogram 4002 (5501): Restoration of the Arm Lowering Mechanism and Installation of a New Tracking Sensor Light Source

I started the restoration of this (exciting) early 5501 type Beogram 4002 that came from the UK to my bench with the rebuilding of the arm lowering mechanism. The first step of this procedure is to remove the solenoid linkages and the damper for inspection/cleaning and re-lubrication. This shows the assembled mechanism:

This shows the disassembled and cleaned components:

This video shows how to rebuild the tone arm mechanism in detail.

The next step is to do the same for the damper-to-arm linkage. In order to get to its pivot point that needs new lubricants, one has to take out the sensor arm:

This shows the arm sideways on a piece of cloth. Removal of the retaining washer and the small spring that is underneath (careful here, if you do that at home...this spring is important but quickly lost) allows the removal of the linkage:

This video shows how to get to the damper to arm linkage and re-lubricate it.

After the linkage is reinstalled, the arm ends to be re-implanted. At this point it is important to get the lateral parallelism properly adjusted:

The arms need to be parallel and perpendicular to the rods on which the carriage travels.

After that the vertical parallelism can be adjusted with a set screw in the back of the arm assembly:

The arms need to be at the same height (I apologize for the slightly unfocused picture taken in the 'heat of battle'...;-).

The final step is to install a new tracking sensor light source. The old lightbulbs are pretty fragile at this point in time, and so the installation of an LED based replacement is recommended to ensure day-to-day use reliability.

This shows the original light source with its black light shield:

I used a SMD LED based replacement part that I designed a while ago. It represents an improvement, not only in longevity, but also in function since it has a Beogram 4000 inspired trimmer that allows adjusting the light intensity. This is very convenient when it comes to the fine tuning of the tracking sensor feedback. I will do this procedure at a later point in time, since a few other things need to be sorted out with this lovely Beogram before I can adjust the tracking mechanism. Here is an impression of the new part installed:

The next steps will be fixing the cracked pulley and the broken end groove detection sensor, and to get the carriage position switches back into spec. 

Beogram 4002 (5501): A New Arrival from the UK

Beolover's joyful summer travel has come to an end! Time to get back to the bench!

Last week a lovely Beogram 4002 (5501) arrived for some TLC from the UK. The exciting part here is that this particular unit is an early style 5501 model that has a few interesting design features that can be regarded as stepping stones between the original Beogram 4000 design and the later 4002 types.

The unit came well packed and shipping was arranged by parcelhero.com. I really like parcelhero. They offer fully tracked express service between the UK and the US. It usually only takes only an impressive 3-4 days door-to-door, and the price is about the same like standard international snail mail. Just outstanding. I really wish we had something like this in the US...

Anyway, after digging out the original B&O box from about 4 cubic yards of bubble wrap (better too much than too little!..;-), I extracted the 4002 from its styrofoam protectors and set it up on my bench:

The overall condition of the unit is pretty good, albeit the keypad has worn areas

and there is a bit of veneer missing from the plinth:

Under the hood is seems pretty original, at least there are no obvious signs of human creativity,

Except that there was a unique grounding wire installation, which used one of the support spring screws as terminal:

The brown cable let do a switch on the outside:

Obviously someone experienced intermittent grounding issues, possibly due to a RCA adapter missing a broken out grounding lead. I removed this construction.

While we are looking at cables, here is a picture of the interesting UK plug that was installed:

Looks a bit like a tea kettle, doesn't it??..;-)

I temporarily exchanged it with a US plug allowing me to operate the unit from a standard US outlet (I also put in temporary 500mA fuses replacing the original 250mA types that are used in the 220-240 environment to account for the double current that will flow while it is operated at 110V).

The exciting parts are the design specifics of this model. This shows the (broken, hence the tape) end groove detection set-up that is mounted on the spindle pulley:

The light bulb illuminates the spindle pulley, which has four holes. Through these the light illuminates a photosensor. This allows the detection of the spindle speed, which can be used to detect that the needle is in the end groove, where the carriage moves faster than usual. This mechanism replaces the servo-voltage based set-up that is used in the Beogram 4000. One could think of this mechanism as an analog rotary encoder...just awesome!

The metal plate in front of the encoder holds the springs that actuate the switches that are used for position detection, similar to the setup found in the Beogram 4000. This was later replaced by an optoelectronic mechanism using a plexiglass bar with blacked out regions to block light from a bulb or IR LED. Here is another view of this setup:

Upon further inspection I found that one of the springs that hold up the bolts that connect the hood hinge to the chassis is missing:

I usually replace these with springs from ball point pens...;-)

After this first look I tried to start the unit up. There were life signs, but the carriage was a bit sluggish...so the mechanical restoration of the carriage drive system and arm lowering mechanisms will be the first items to look at when I start this restoration.

Beogram 4000: Keyboard Keys - Video About Removal and Installation

A Beogram 4000 that I recently sent out after restoration arrived with two keys detached from the keypad. I had taped them down and put a foam pad on top so that the hood would press them down, but two still came loose.

This is a little bit a design flaw of the 4000, since its beautifully large (and therefore heavy) keypad keys are only attached by leaf springs. This is great as long as the unit sits on your sideboard, but the rigors of shipping can be too much for this mechanism. I wanted to avoid another round trip of this beauty, and so I decided to design special installation tools for my customer, and I made a video how to use them. The video shows how to remove the keys, and how to get them back in. Like all my part designs, the tools are available to other B&O enthusiasts. They are plastic, i.e. there is little risk to damage the precious brushed aluminum surfaces. The tools also work much better than the usually employed flat head screwdrivers. Check out the video:

Beomaster 8000 Terminal: Replacement of Corroded Battery Terminals and the Design of a New 3D Printed Battery Cover

The Beomaster 6000 that I just repaired came with a non-working Beomaster 8000 Terminal remote control. It turned out that a simple replacement of the corroded battery terminals was enough to restore power and with that the functionality of the unit. However, this Terminal was also lacking the battery cover and the rubber bumpers that keep it from sliding off polished furniture surfaces. Since this is not the first Terminal that I saw with lacking battery compartment cover, I decided to design a 3D printed replacement part. Here are a few impressions of my progress:

This shows the original corroded battery terminals:

and the installed replacement:

After a few design iterations I had a fitting battery compartment cover:

This shows it in comparison with the cover I extracted from one of my Terminals. Here the outside surface of the part:

The part has rubber bumpers like the original. Thir location is slightly different due to stability considerations, but they do their job very well.

This shows the part installed:

Pretty, eh?? The latch works exactly like in the original part. The cover can be extracted from the ouside by inserting a small flat blade screw driver and then lifting it out.

But why in orange you may wonder?!? I usually use orange for prototyping since I have an ample supply on hand these days for filling CleanerVinyl orders. Orange also reveals more details than black in photographs. But of course the final version was printed in black. Here in comparison with the original:

And in more detail:

If you are lacking the battery compartment cover on your Terminal, this part is available for purchase. Just send me message (use the contact form on the left).

The remaining task was to replace the worn/missing rubber bumpers at the lower end of the Terminal body. This shows a newly installed bumper (right) in comparison with a broken off original bumper (left):

And both replaced:

The final step was to clean the unit. I employed my ultrasonic cleaner (another benefit of the CleanerVinyl project...;-) and the buttons and housing came out in a fairly pristine condition:

What a lovely classic design! This is Beolove!

Beomaster 6000 (2253): Rebuilding Output Amplifier and Power Supply, and Adjustment of Quiescent Current and Amplifier Offset

After replacing the volume belt in the Beomaster 6000 (2253) that I am repairing right now, the basic functionality was re-established. However, I noticed the the output got hot quickly without playing the unit very loudly. This was a certain sign that the quiescent current (no load current) was too high and that adjustments needed to be made. Once the board is up, it is a great idea to replace the electrolytic capacitors and upgrade the output trimmers to modern 25x turn encapsulated units. The next step is to also replace the reservoir capacitors in the power supply. They see elevated temperatures and have a tendency to go bad at this point in time. So, lets do it:

Here is a picture of the output (left) and power supply (right) boards:

The picture looks a bit 'jagged' since I used the 'pano' function of my iPhone camera app to capture the entire unit in one picture from a close-up distance.

The output amplifier board can be easily accessed via loosening two screws from the bottom of the unit that hold the heatsink down. Once they are unscrewed the entire heat sink with board can be pulled up and put into service position (use the foam piece that sits on the reservoir caps of the power supply if it is still in there to prop the board up. After removing the various plugs the unit can be extracted:

Removal of the five screws that hold the board to the sink allows to flip the board over to access the solder points:

This makes it straight forward to replace the electrolytic capacitors and the two output trimmers:

Note that the output trimmers should not have more than 50 Ohms across the relevant pins when you put them in. If they exceed 60-70 Ohms or so the current will be pretty high in the output transistors and damage may occur when the unit is switched on. At 50 Ohm you will see about 3 mV across the emitter resistors.

Then it is time to put the assembly back in and adjust the quiescent current by increasing the trimmer resistance a bit. I usually put them in in an orientation that CW adjustment increases the quiescent current:

The voltage across the emitter resistors of the output transistors needs to be 22 mV. 

After doing this also for the right channel, I then adjusted the amplifier offset to make sure that there is no DC on the speaker outputs. This is done by hooking up the probes across the output connectors

and adjusting the offset trimmer to until 0 mV is measured. This is usually achieved with a close-to-center trimmer position:

After finishing up the output board, I turned my attention towards the power supply. It can also be lifted up via unscrewing two screws that hold the heat sink from underneath the unit, but there are two more screws that hold the PCB on top. This shows the power supply in its original condition:

The reservoir capacitors for the smaller voltages are on the board. They are of the 'multiple negative contact pads type' that was used in many B&O types of this vintage:

While these caps can be exchanged with standard model types (the multi connector types do not seem to be made anymore) but care needs to be taken since some designs utilize the multi connectors to elegantly bridge traces on the PCB, thereby saving on the use of jumpers. This is the case with C1 (3300uF) on the power supply board. Usually the negative lead of the capacitor can be used to make the bridge. This is shown here (vertical wire bridge on the left side of the positive C1 solder point):

On the right you see the solder points of the C10 (2200uF) replacement. There no bridge is necessary since two of the contacts ended up in dummy pads that are only there to give the can more stability.

On to the main reservoir caps of the ±50V rails. This shows them in their original condition:

The right one shows signs of corrosion (dark bulge about 10 O'clock). I replaced them with modern 105C grade Panasonic units that are 5 mm 'thinner' than the original 40mm cans. this made it necessary to roll them in some cardboard to maintain mechanical stability in their compartment:

This shows the completed power supply:

and a detail shot of the two on-board reservoir caps:

all good now in the heat sink compartment! This Beomaster should be good for another number of years. Usually there are no issues with the capacitors on the other boards since they run much cooler than the boards in the heat sink area. The LED displays of this unit are miraculously still working on all segments (another major trouble spot, but luckily this is only a cosmetic issue and not essential for the operation of the unit)...so let's hope that they will do that for some longer!

Beomaster 6000 (2253): First Contact and a New Volume Belt

A Beomaster 6000 (2253) arrived on my bench for some TLC. It came with an indication of 'the volume adjustment makes strange noises'. I opened it up and as expected I found a slack volume servo belt that was not able to drive the volume potentiometer all the way anymore due to slipping. This phenomenon was responsible for the noises when the potentiometer got stuck. I replaced the belt with an EPDM O-ring of the correct size and that restored the volume function. Here is an impression of the new belt installed:

While I tested the units other functions I noticed that the heat sink very quickly developed a pretty high temperature in the center area. This indicated that the right channel at least runs at a too high quiescent current. This is a common phenomenon in this generation of Beomasters due to the often corroded quiescent current adjustment trimmers. As they increase their resistance due to the formation of an oxide film the current gets ramped up. In the extreme this results in a burn out of the output transistors of the respective channel. This means this Beomaster should quickly receive modern multi-turn encapsulated trimmers for long-term stability.

Beogram 8002: First Contact, Exchanging the Electrolytic Capacitors and a Lesson About the Importance of Decoupling Capacitors for Microcontrollers

I recently obtained a Beogram 8002 in decent cosmetic condition. As usual, the aluminum panels had come loose, though:

After loosening the transport locks, decoupling the suspension springs, taking out the plate below the arms and removing the two screws that hold the top part of the enclosure to the bottom part on the left, I put the unit into service position. Then I plugged it in. Nothing. No red LED dot in the display and no response to any of the buttons. It appeared that, as is often the case with unadulterated Beogram 8002 (or 8000) that come out of storage, the reservoir capacitors of the power supply had gone bad. This usually prevents the processor from operating and that is the end of it.

I decided to replace all electrolytic capacitors and then do some more troubleshooting in case that would not fix the issue.

This shows the circuit board after removing it from the Beogram:

Here some details. This shows the reservoir capacitors of the power supplies:

I replaced all the electrolytic capacitors with quality Japanese 105C grade units:

There is one more big capacitor that needs replacing. It is located in the power transformer 'brick' that can be removed from the units and allows configuring them for different grid voltages. This shows the original 47uF unipolar capacitor (C1):

This capacitor acts as coupling capacitor for the two linear motor coils and gives them the desired phase shift. This is similar to the phase shift capacitor found in the AC motor Beogram 4002 and Beogram 4000 models which have run on two-phase motors. Probably due to the large size of 1980s unipolar capacitors this unit was put into the power brick. I replaced it with two modern bipolar 100uF units connected back to back in series:

Due to their small modern size it was necessary to design a fixture to hold them in place. I designed a 3D printed part that filled the vacant space in the power brick:

What was left after exchanging these capacitors were the two 5V voltage regulator capacitors soldered directly to the board that holds the 5V regulator and the +15V TIP32 transistor mounted to the bottom of the enclosure for heat transfer purposes. Unfortunately, I forgot to take pictures of these caps.

The final capacitor to exchange was the sole 47u electrolytic decoupling capacitor in the uProcessor can. It sits under the small board that holds the 4013 flipflop (IC7) that stores the tacho disk readout coming from the speed sensor (IC1) for evaluation by the microcontroller.

This shows the original capacitor after pulling up the flipflop board:

I replaced it with a new capacitor:

Note the solder point to the left of the capacitor where it is supposed to connect to GND. I forgot to solder it on the upper side, and that is where an interesting journey began that allowed me to 'explore' the 8000 and 8002 Beograms a bit more in depth...;-).

At this point I finally put the PCB back into the Beogram and then plugged it in. On the positive side it gave me a life sign on the display, indicating that power was restored. On the negative side the life sign was not a singular LED dot indicating readiness to operate, but it showed me "0.0.0.0." instead. Pressing buttons on the keypad yielded no response. Disappointing! 

I unplugged it and then plugged it back in and the display showed "1.1.1.1.". Very mysterious I thought! After a few more plugging in and outs it assumed the normal state and I was able to activate "Play". The arm started moving and everything seemed fine. Well, I repeated the plugging cycle one more time and I was back to "0.0.0.0.". At this point it dawned on me that the microcontroller had a hard time to start into its 'ground state' when power was connected, and that it rather entered a random state preventing it from executing its firmware. Since it seemed to occasionally end up in the proper state and then worked, I thought there was a problem with the controller itself. So I did an interesting experiment:

Since I only had one 8002 at hand but several 8000s, I extracted the uProcessor from a 8000 and plugged it into the 8002 instead of its original processor. The result was that nothing changed. Occasionally it would work but mostly not. I then replaced the entire 8002 processor can with the one from the 8000. And everything was normal! This is an interesting result by itself since it establishes that one can indeed run a 8002 with the processor of the 8000. Even the "<" and ">" arrows on the 8002 sensor arm work properly since they get their power via an analog circuit that depends on the direction of the carriage movement. There may still be some minor differences with regard to updated operational or control behaviors but basically the 8000 processor seems to have a very similar if not the same firmware on it.

This told me that the 8002 processor was o.k. but that it had a difficult time to reset during the establishment of the 5V power rail during power-up. I then figured out that by manually resetting the processor (via briefly connecting the junction between R74 and R76 to GND) after plugging the deck in, I was able to reliably start it up into the 'ground state' and after that everything seemed normal.

All this finally got me thinking about the power supply of the processor and I finally realized that the 47u coupling capacitor was not connected to GND due to the missing solder point on the component side, which is the only connection to GND of this capacitor. The bottom solder point is not connected, i.e. is only there for mechanical stability. 

I added some solder to the top point and then the deck worked (mostly) normally. The only issue I could see immediately was that the carriage moved at significantly different speeds in in- and out-directions. But this is the topic of another post...